In controlling the driving of a HVAC (Heating, Ventilation and Air Conditioning) motor and a battery cooling fan motor, rotational speed feedback control may be needed for the purpose of (1) adjustment of the amount of conditioned air by automatic air conditioning, (2) adjustment of the amount of cooled air in response to an increase in battery temperature, and (3) prevention of change in the amount of air due to variation of a power supply or a load, and so on.
For the rotational speed feedback control, unavoidable hunting (variation of rotational speed) occurs when the motor is rotated at a low speed. In order to avoid such hunting, existing motor driving devices have employed a method of masking rotational speed feedback control and switching the rotational speed feedback control to open control or a method of stopping the driving of the motor when the motor is rotated at a low speed.
However, the method of masking the rotational speed feedback control has a problem in that the rotational speed fluctuate when the rotational speed feedback control is switched to the open control. Further, since a rotational speed to arouse hunting may fluctuate depending on the number of poles of the motor, it may be difficult to avoid hunting with existing methods.
In a related art, a motor control circuit for selectively setting a control gain which is suitable in low speed rotation or in high speed rotation of the motor is described. However, the motor control circuit is configured to switch the control gain in response to a switching signal associated with an external input signal. That is, the motor control circuit may not switch the control gain based on its internal condition.